Heat-resisting material and conveyer belt using same

Abstract: A three-layer heat-resistant material is disclosed which includes a substrate of a carbon fiber-reinforced carbon composite (1), an outer metal layer (3) and a ceramic layer (2) interposed between the substrate and the metal layer. A conveyer belt using the heat-resistant material is also disclosed.

Description: This invention relates generally to a heat-resistant material and, more specifically, to a three-layered material having a carbon fiber-reinforced carbon composite layer, a ceramic layer and a metal layer. The present invention is also directed to a belt conveyor using the heat-resistant material. A heat-resistant alloy has been hitherto employed for parts which are subjected to high temperature conditions. One problem of such a heat-resistant alloy part is that a deformation thereof occurs upon repeated use, due to thermal expansion and shrinkage. Carbon fiber reinforced carbon composites (hereinafter referred to as C-C composites) are now increasingly used in various fields because of their good heat-resistance and high mechanical strength. One problem of such a C-C composite, however, is that chemical deterioration occurs upon contact with steam, carbon dioxide or oxygen. Thus, machines using such heat-resistant alloys or C-C composites for parts thereof which are subjected to a high temperature of, for example, 1000°C, require repeated repair and maintenance work due to deterioration of the parts. In view of the state of the art it would be desirable to provide a heat-resistant material having improved resistance to heat and to gases such as steam, carbon dioxide and oxygen. EP-A-0548864 discloses a method for forming, in situ , a well-bonded outer layer of aluminum on a C-C composite by means of an intermediary bond of an intermetallic metal carbide interface of tantalum, titanium or hafnium. The heat-resistant material in accordance with the present invention comprises a substrate of a carbon fiber-reinforced carbon composite; an intermediate layer of a ceramic provided over a surface of said substrate, wherein said ceramic is at least one member selected from silicon carbide, zirconium carbide, tungsten carbide, titanium nitride, zirconium nitride, aluminum nitride, boron nitride, silicon nitride, alumina, titania, chromia and silica; and an outer layer of a metal provided over a surface of said intermediate layer; said intermediate and outer layers having thicknesses of 2-300 µm and 0.2-3 mm, respectively. In another aspect, the present invention provides a conveyor belt comprising a plurality of parallel, laterally extending, spaced apart supporting rods, and link means formed of a metal and extending between each adjacent two of said supporting rods to link said adjacent two supporting rods, said link means being rotatably engaged by each of said adjacent two supporting rods, wherein each of said supporting rods is formed from the above-defined heat-resistant material of this invention. As noted, the heat-resistant material of this invention has an intermediate ceramic layer and an outer layer of metal, and both layers have a specific thickness. It has been found that such a material shows resistance to heat and gases for a long period of time. In contrast, a composite material in which the C-C composite substrate is coated directly with a steel layer has been found to lack these properties because the C-C composite reacts with the steel. It has been also found that a composite material in which the C-C composite substrate is coated only with a ceramic layer also fails to achieve the desired properties because pin holes are formed in the ceramic layer upon being subjected to high temperatures for a long period of time. The invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 is a perspective view, cut away in part, diagrammatically showing a preferred embodiment of a heat-resistant material according to the present invention in the form of a rod; Fig. 2 is a fragmentary plan view schematically showing an embodiment of a conveyer belt using a heat-resistant rod of Fig. 1; and Fig. 3 is a fragmentary, perspective view schematically showing another embodiment of a conveyer belt of the present invention. Referring to Fig. 1, designated generally as 10 is a heat-resistant material according to the present invention. The material 10 is composed of a substrate 1 of a C-C composite in the form of a rod. The substrate 1 may be any other desired form such as a pipe, a plate or a block. The C-C composite is a material in which a multiplicity of carbon fibers are dispersed in a carbonaceous matrix. A number of methods are known for the fabrication of C-C composites. Typical examples of such methods include (a) a CVD method wherein a hydrocarbon gas is fed to a furnace in which a carbon fiber preform is placed and heated at a high temperature, thereby to pyrolyze and carbonize the hydrocarbon gas and to permit the thus produced carbon to deposit on the carbon fiber preform, (b) a method wherein carbon fibers impregnated with a thermosetting resin such as a phenol resin or an epoxy resin is molded into a desired shape and the molding is then calcined in an inert gas to carbonize the resin and (c) a method which is disclosed in United States patent No. 4,772,502 and in which a preformed yarn, including a core of a multiplicity of carbon fibers into which mixed powder of carbonaceous pitch and coke is dispersed, and a flexible sleeve of a thermoplastic resin surrounding the core, is formed into a desired shape by hot pressing or filament winding and the shaped body is then calcined. Any known C-C composite may be suitably used for the purpose of the present invention. Provided on a surface of the substrate 1 is an intermediate layer 2 of a ceramic having a thickness of 2-300 µm, preferably 5-100 µm. A thickness of the ceramic layer 2 of below 2 µm makes it difficult to prevent the reaction of the substrate with a metal layer 3 provided over the intermediate ceramic layer 2. Too large a thickness in excess of 300 µm is, on the other hand, undesirable because delamination of the ceramic layer is apt to occur upon being subjected to high temperature conditions. The ceramics used for the intermediate layer 2 are silicon carbide, zirconium carbide, tungsten carbide, titanium nitride, zirconium nitride, aluminum nitride, boron nitride, silicon nitride, alumina, titania, chromia and silica. The ceramic layer 2 may be formed on the substrate 1 by any suitable method such as a CVD (chemical vacuum deposition) method, a PVD (physical vacuum deposition) method, an ion plating method, a sputtering method, a thermal spraying method, a laser vacuum deposition method, a plasma spraying method, a plating method or a coating method. The ceramic layer 2 is covered with the outer metal layer 3. The metal layer 3 is formed of a heat-resisting metal such as carbon steel, a steel alloy, e.g. stainless steel, molybdenum steel or nickel steel, a non-ferrous metal, e.g. aluminum, nickel or copper, or an alloy of a non-ferrous metal. The thickness of the metal layer 3 is 0.2-3 mm, preferably 0.4-2 mm. A thickness of the metal layer 3 of less than 0.2 mm is insufficient to provide satisfactory mechanical strength. When the thickness exceeds 3 mm, the resulting heat-resistant material 10 is apt to be deformed upon repeated use at high temperatures. The metal layer 3 may be formed on the ceramic layer 2 by any suitable method such as a CVD method, a PVD method, an ion plating method, a sputtering method, a laser vacuum deposition method, a plasma spraying method or a plating method. When the substrate 1 is in the form of a relatively short rod, the metal layer 3 may be formed by inserting the substrate (core) 1 having the intermediate layer 2 into a previously prepared metal pipe which serves as the metal layer 3. As a consequence of the above-described three-layered structure, the heat-resistant material 10 according to the present invention exhibits good heat resistance for a long period of time. In particular, the outer metal layer 3 can impart to the material 10 excellent resistance to gases such as O 2 , CO, CO 2 and steam. The provision of the ceramic intermediate layer 2 can prevent the reaction between the C-C composite substrate 1 and the metal layer 3. Further, the C-C composite layer 1 can prevent the metal layer 3 from deforming during use. Moreover, even when pin holes are formed in the intermediate ceramic layer 2 during use, the metal layer 3 can protect the C-C composite substrate 1 from the attack by reactive gases. In addition, the heat-resistant material is light in weight and has a reduced heat capacity, contributing to the saving of energy consumption. The dimensional stability of the heat-resistant material permits the use thereof in an automated machine. Thus, the heat-resistant material 10 according to the present invention lends itself to many applications, such as in the fabrication of jigs, heat rollers, conveyer belts and holders. Fig. 2 and Fig. 3 depict one such application of the heat-resistant material 10 of the present invention ie to form a conveyor belt. The embodiments of conveyor belt shown in Figs. 2 and 3 include a plurality of parallel, laterally extending, spaced apart supporting rods 10, and link means 11 or 12 formed of a heat-resisting metal and extending between adjacent two of the supporting rods 10 to link the adjacent two supporting rods 10 such that each of the link means 11 or 12 is rotatable about respective supporting rods 10. Each of the supporting rods 10 is formed from a heat-resistant material according to the present invention. In the embodiment shown in Fig. 2, the link means 11 is a coil wound around adjacent two supporting rods 10. In the embodiment of Fig. 3, two adjacent supporting rods 10 are linked by a plurality of rings 12. The following examples will further illustrate the present invention. Example 1 A multiplicity of C-C composite rods each having a diameter of 9 mm and a length of 600 mm were each coated with silicon carbide by powder coating method to form a 40 µm thick ceramic layer. The powder coating was performed by static coating of a powder coating composition containing silicon carbide powder and a phenol resin binder, followed by a heat treatment. Each of the coated rods was inserted into a SUS 304 stainless steel pipe having an outer diameter of 10.2 mm and a thickness of about 0.5 mm. After the insertion, both ends of each pipe were closed by welding. The rods were then formed into a cubic basket of a 600 x 600 x 600 mm size by welding. A pair of metal parts were temporarily bonded with a solder paste and placed in the basket. The basket was then fed to a heat-treatment zone maintained at 1,160°C and under a gas stream containing 2% of CO, 10% of CO 2 , 2 % of H 2 and 86 % of N 2 and, subsequently, to a cooling zone so that the two metal parts were firmly bonded with each other. The above heating and cooling process including loading and unloading of the metal parts was carried out in an automatic mode. It was found that the basket was free of deformation and usable even after 1 year use. Comparative Example 1 Example 1 was repeated in the same manner as described except that the basket used was formed from SUS 304 stainless steel rods (diameter: 10.2 mm, length: 600 mm). Deformation of the basket was so significant that the test was stopped about 1 month after the commencement of the test. Comparative Example 2 Example 1 was repeated in the same manner as described except that the basket used was formed from C-C composite rods (diameter: 10.2 mm, length: 600 mm). Deterioration of the basket was so significant that the test was stopped about three weeks after the commencement of the test. Comparative Example 3 Example 1 was repeated in the same manner as described except that the C-C composite rods were inserted into respective SUS 304 stainless steel pipe without coating with the silicon nitride ceramic. Deterioration of the basket due to the reaction of the metal layer with the C-C composite and to the reaction of the gases with the C-C composite was so significant that the test was stopped about 5 months after the commencement of the test. Example 2 A multiplicity of C-C composite rods each having a diameter of 5 mm, a length of 500 mm, a bending strength of 392 MPa (40 kgf/mm 2 ) and a density of 1.70 g/cm 3 were each coated with alumina by thermal spraying method to form a 50 µm thick ceramic layer. Each of the coated rods was immersed in a nickel plating bath to form a nickel layer having a thickness of about 0.5 mm over the ceramic layer. Using the supporting rods thus obtained, an endless conveyer belt having a circumferential length of 40 m and a structure as shown in Fig. 2 was prepared. Each adjacent two supporting rods were linked with a coil formed of SUS304 stainless steel and having a diameter of 4 mm. The space between each adjacent two supporting rods was 40 mm. The thus obtained conveyer belt was mounted on a conveyer disposed in an oven. The conveyer was driven at a running speed of 1 m per hour. The oven was maintained at 1,150°C and in an atmosphere containing 1.5 % of CO, 13% of CO 2 , 1 % of H 2 and 84.5 % of N 2 . It was found that the conveyer belt was free of deformation and usable even after 1 year use.

Claims: A heat-resistant material comprising a substrate of a carbon fiber-reinforced carbon composite; an intermediate layer of a ceramic provided over a surface of said substrate, wherein said ceramic is at least one member selected from silicon carbide, zirconium carbide, tungsten carbide, titanium nitride, zirconium nitride, aluminum nitride, boron nitride, silicon nitride, alumina, titania, chromia and silica; and an outer layer of a metal provided over a surface of said intermediate layer; said intermediate and outer layers having thicknesses of 2-300 µm and 0.2-3 mm, respectively. A heat-resistant material as claimed in Claim 1, wherein said metal is at least one member selected from steel, a steel alloy, aluminum, an aluminum alloy, copper, a copper alloy, nickel and a nickel alloy. A heat-resistant material as claimed in Claim 1 or Claim 2, in the form of a rod, a plate, a cylinder or a block. A heat-resistant material as claimed in any preceding claim, wherein said intermediate and outer layers have thicknesses of 5-100 µm and 0.4-2 mm, respectively. A heat-resistant material as claimed in any preceding claim, wherein said substrate is in the form of a rod, wherein said intermediate layer surrounds said substrate, and wherein said outer layer surrounds said intermediate layer. A conveyer belt comprising a plurality of parallel, laterally extending, spaced apart supporting rods, and link means formed of a metal and extending between each adjacent two of said supporting rods to link said adjacent two supporting rods, said link means being rotatably engaged by each of said adjacent two supporting rods, wherein each of said supporting rods is formed from a heat-resistant material according to Claim 5.

Inventors: NAKAGAWA TAKAO, TACHIBANA MASAHARU, NAKAGAWA, TAKAO, TACHIBANA, MASAHARU
Applicants: ACROSS CO, ACROSS CO., LTD.
Application year: 1994
Main classification: C04B41
IPC codes: C04B41, F27D3